# 实现斐波那契数列
**所谓的斐波纳契数列是指**：
前 2 个数是 0 和 1 。
第 i 个数是第 i-1 个数和第 i-2 个数的和。
**斐波纳契数列的前 10 个数字是**：
```
0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ...
```
#### 怎样算解成功：
给定 1，返回 0
给定 2，返回 1
给定 10，返回 34
#### 题目分析：
## 递归实现
```javascript
const f = (num) =>{
if(num === 1) return 0
if(num === 2) return 1
return f(num-1) + f(num-2)
}
```
## 非递归实现
```javascript
const f = n => {
let num = new Array(n).fill(0); // 初始化数组，并设置初始值
num[1] = 1; // 设置第二个元素的值 推导第3个元素
for (let i = 2; i <= n - 1; i++) {
num[i] = num[i - 2] + num[i - 1]; // 遍历逐步推导元素值 数组完全符合数列不用进行判断等 运行效率最高。
}
return num[n - 1]; // 数组是从0开始计算 所以要减1
};
```
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